“I condemn the brutal slaying of Boris Nemtsov in the strongest terms possible. The gangland-style murder of a leading Russian dissident on the streets of Moscow raises the question of whether bullets have replaced the ballot box in Russia, and whether any peaceful opposition voice is safe. We mourn Mr. Nemtsov’s death and send our deepest condolences to his family and friends.”

According to Russian officials, Mr. Nemtsov was shot four times in the back on a street near the Kremlin. A leader of Russia’s political opposition, he was a co-founder of Solidarity and a key organizer of a scheduled March 1 protest in Moscow.

Mr. Nemtsov served as First Deputy Prime Minister of Russia under President Boris Yeltsin. He spoke at a Helsinki Commission event in Washington in November 2010 at the world premiere of the film “Justice for Sergei.”